Railway switches generally include a switch machine mounted on the outside of the rails adjacent the turnout points. The switch machine actuates a throw rod that is connected to a switch rod extending between the switch points.
A lost motion device, commonly referred to as a basket, may be provided between the throw rod and the switch rods to take up some of the motion of the throw rod before transmitting it to the switch rods. The basket enables a signal maintainer to adjust both the initial position and the throw of the switch rod to account for differing design applications of the rods and the total linkage length of the rod and to compensate for differing design locations of the switch machine in relation to the switch point.
In order to ensure coordinated movement between the point and heel ends of the movable rails, assist rods are used with longer switch points. For convenience the point and heel ends of the assembly are referred to as the front and rear ends respectively. The assist rods act to transfer force from the front end switch rods to those at the rear end. Operating or throw rods extend from the switch rods to the assist rod. The assist rod extends along the outside of the running rail, but on the side of the tracks opposite to the switch machine. This is done to accommodate the clearance requirements between switch accessories and the rail (to allow for tamping and protection from dragging equipment on passing trains). Juxtaposing the switch machine and the assist rod would require unusually long ties to maintain the necessary clearance.
In a typical arrangement, the throw rod is connected to the switch rods by means of a basket. The switch rods are in turn connected to the switch point (rails). The switch rods are also connected to a connector rod that extends under the running rail to a crank stand located on the outside of the running rail. The crank stand includes a lever, one end of which is connected to the connector rod and the other end of which is connected to an elongated assist rod running parallel to the running rail. The lever is mounted on a hinge on the crank stand such that when the connector rod causes one end of the lever to rotate about the hinge, the other end causes axial displacement of the assist rod. The assist rod is attached at its rear end to a similar lever and crank stand assembly that is in turn connected to a connector rod. The rear end connector rod is connected to a basket which transfers movement of the connector rod to the rear end switch rods.
It has also been proposed to used a torsional assist rod mounted on the side of the track that is distal from the switch machine. The assist rod is connected by a pin to the end of the switch rod or to the end of a connector rod. Displacement of the front end switch rod causes the assist rod to rotate. By a similar arrangement at the rear end, rotation of the assist rod throws a connector rod connected to the rear end switch rod. It is also known to locate torsional assist rods between the rails.
One disadvantage of prior art assist rod assemblies is that the basket is located between the rails to allow for tamping on the outside of the rails. However, the location of the baskets between the rails results in limited accessibility due to hot air ducts used for snow removal that are frequently mounted between the rails over the top of the basket. In addition, the signal maintainer must place himself in the direct path of oncoming rail traffic to service or adjust the device.
In addition, the switch ties must accommodate both a switch machine (on one end) and an assist rod and its associated linkage components (on the other end). As a result, relatively long ties (typically 14 feet long) are needed. In the case of crowded rail yards, the loss of space resulting from adjacent switches becomes critical.
It is an object of the present invention to provide an improved assist rod assembly that overcomes the foregoing deficiencies.